Phase I of a clinical study of Ukrain was performed in 19 healthy outpatient volunteers. Their general clinical conditions were evaluated, as well as the following parameters: biochemical, haematological, immunological, electrolyte and trace elements, neopterin, immune complexes and non specific blocking factors. Ukrain was administered intramuscularly (i.m.) or intravenously (i.v.) every one, two or three days in doses of 5 to 50 mg for 7 to 40 days. In one case the drug was administered for three years in the dose of 5 to 50 mg/injection in repeated courses. During the investigation no significant changes were found in clinical states. During the intramuscular injections the volunteers felt only localized pain; some reported drowsiness, increased thirst and polyurea. There was a slight, insignificant increase in body temperature and negligible decrease of blood pressure in some cases. In conclusion, it can be said that Ukrain is well tolerated in healthy volunteers in the doses of 5, 10, 20, and 50 mg/injection, even during prolonged (up to three years) administration.